1. Field of the Invention
The invention relates generally to door alarm systems and more particularly to a door alarm system including a door lock assembly having an interior trim piece having a request to exit (REX) switch for generating a REX signal in response to a rotation on an interior handle where the REX switch is mechanically isolated from a forcing movement on the exterior side of the door lock assembly.
2. Description of the Prior Art
Door alarm systems are used for generating an alarm signal when a door into a secure area is forced open from outside the secured area. The alarm system typically includes alarm shunts so that a false alarm signal is not generated when the door is open for an authorized entry into the secured area or when a request to exit (REX) switch generates a REX signal as a result of the door being opened from the inside.
Existing door lock assemblies of a cylindrical type incorporate the REX switch in a latch retractor within a central chassis body of the assembly. However, such cylindrical door lock assemblies are known for generating false REX signals in response to a forced movement of the exterior side of the door lock assembly when a door is forced open. This false REX signal prevents the proper alarm signal from being issued for a forced entry into the secured area. An attempt has been made to solve this problem by using an infrared generator with an detector as the REX switch. The infrared detector detects either a broken beam or beam reflection from the generator or Doppler shift due to motion of an object reflecting the beam. However, this solution has the undesirable side effect that someone inside the secured area near to the door may unintentionally cause the infrared detector to generate a false REX signal, thereby enabling someone outside the secured area to force the door without causing the alarm signal to be given.
There is a need for a door alarm system and a door lock assembly that generates a request to exit (REX) signal in response to a rotation of an interior door handle where the movement of the door lock assembly due to a force applied on the exterior side does not result in a false generation of the REX signal.
It is therefore an object of the present invention to provide a door alarm system where an interior trim piece of a door lock assembly includes a request to exit (REX) switch that is mechanically isolated from the exterior side of the door lock assembly so that a forcing movement applied to the exterior side of the door lock assembly is prevented from causing a false generation of the REX signal.
Briefly, in a preferred embodiment, an alarm system of the present invention includes a door detector, an entry request device, a door lock assembly, and a control unit. The door detector provides an open door signal when a door is open. The entry request device provides a request to enter (REN) signal having an authorization code in response to a request by a user on the exterior of an area secured by the door to enter the secured area. The control unit checks the validity of the authorization code. When the code is valid, the control unit issues a lock control signal to the door lock assembly for unlocking the door. The door lock assembly includes an interior trim piece having a request to exit (REX) switch. The REX switch automatically provides a request to exit (REX) signal when a user within the secured area uses the door lock assembly to exit the secured area. The control unit issues an alarm signal when it receives the open door signal unless it also receives either the REN signal having a valid authorization code or the REX signal.
A cylindrical door lock assembly of a preferred embodiment includes an exterior trim piece, a door lock chassis, a latch, and the interior trim piece. The chassis includes a central fixed chassis body for receiving the lock control signal, an interior spindle, and an exterior spindle. The interior and exterior spindles rotate independently within the chassis body for operating a latch retractor for retracting the latch.
When the lock control signal is in the unlocked state, a rotation of the exterior spindle by an exterior handle operates latch retractor for retracting the latch. When the lock control signal is in the locked state, the exterior spindle is prevented from rotating and the latch cannot be retracted. On the other hand, a rotation by an interior handle rotates the interior spindle operates the latch retractor causing the latch to retract regardless of the state of the lock control signal and also causes the REX switch to generate the REX signal.
The interior trim piece in a preferred embodiment is known as a rose or spring package. The rose (or spring package) includes a housing having an inner aperture, an interface linkage including a switch actuator plate, a spring, and the REX switch. The housing is fixed to the door and the REX switch is fixed to the housing. The interior spindle passes through the inner aperture for connection to the interior handle. The switch actuator plate revolves about a center axis of the interior spindle in response to the rotation of the interior handle. The spring urges against the rotation of the handle and returns the handle to its normal angle when no external torque is applied. The REX signal is generated when a tab or notch on the switch actuator revolves past the REX switch.
An advantage of the present invention is that the REX switch is mechanically isolated so that a force on an exterior side door handle causing movement of the exterior spindle of a door lock assembly does not cause a false generation of a request to exit (REX) signal that would shunt an alarm signal when a door is forced open from the exterior side.
These and other objects and advantages of the present invention will no doubt become obvious to those of ordinary skill in the art after having read the following detailed description of the preferred embodiments which are illustrated in the various figures.